[ACA-4436] - added option for select item to display None (#7113)

* [ACA-4436] - added option for select item to display None

* [ACA-4436] - added unit test and fixed wrong default behaviour

* [ACA-4436] - fixed property check

* [ACA-4436] - fixed unit test

* [ACA-4436] - fixed unit test

lib/content-services/src/lib/content-metadata/services/content-type-property.service.ts

@@ -85,7 +85,8 @@ export class ContentTypePropertiesService {
             value: currentValue,
             key: 'nodeType',
             editable: true,
-            options$: options$
+            options$: options$,
+            displayNoneOption: false
         });
 
         return contentTypeCard;